Cruz can only win the nomination if Rubio (and probably Kasich) drop out and let him compete one-on-one on March 15th. If Trump wins most of the March 15th states like this again, because they are almost all winner-take-all, the delegates Cruz needs ti catch up will be insurmountable. He could still get Trump into a contested convention, but not win outright.
Perhaps that is why Cruz has hitched his wagon to the Bush Dynasty.